Bluespotted ribbontail ray (Taeniura lymma), mostly found in the waters of South East Asia, is not exactly endangered but due to overfishing and habitat loss, it is at the threat of extinction.
redang
Lions Mane Jellyfish

Dance of the jelly fish. Sea creatures, or rather any animal, are only dangerous when they feel threatened. If you treat them with respect and respect their personal space, they will not attack.